Electromagnetic components such as a motor, or inductors such as a choke coil, reactor and the like have a structural unit in which a coil of an electric conductor is formed around a magnetic core. For the magnetic core, soft magnetic materials of various shapes such as a plate shape, foil shape, powder shape and so on are used. Among them, the soft magnetic materials of a plate shape and foil shape are used as a laminated magnetic core. Because the laminated magnetic core is obtained by laminating the soft magnetic material of a plate shape or a foil shape, the shape of the laminated magnetic core is limited to two-dimensional shape, and the orientation of the magnetic flux is also limited to the direction parallel to the plate surface or the foil surface.
On the other hand, because the powder magnetic core obtained by forming work of the soft magnetic powder can be formed into optional shapes by changing the mold shape, the shape of the powder magnetic core can be designed three-dimensionally. Also, because the powder magnetic core has no directionality of the magnetic flux which the laminated magnetic core has, magnetic characteristic is isotropic, and three-dimensional design of the magnetic circuit becomes possible. Because the orientation of the magnetic flux largely affects the characteristics such as the torque in electromagnetic components such as motors, when three-dimensional magnetic circuit is achieved using the powder magnetic core, the characteristics of the electromagnetic components can possibly be improved by the effect of the shape of the magnetic core, and the motor and the like using the magnetic core have been watched in recent years.
Because the electromagnetic components such as a motor and inductor are often used in the AC magnetic field, when the powder magnetic core is used for a motor, inductor and the like, from the viewpoint of improving the electromagnetic conversion characteristic, reduction of the iron loss is required.
The iron loss is defined as the energy loss inside a magnetic body caused when the AC magnetic field is applied to the inside of a ferromagnetic body. In the inside of the material and in the region where the relaxing phenomenon of the magnetic flux change (magnetic resonance and the like) does not accompany, the iron loss is expressed by the sum of the hysteresis loss and the eddy current loss. The hysteresis loss is the minimum energy required for changing the magnetic field orientation inside the material, and, as the coercive force that is a threshold value of the magnetic field change is smaller, the value of the hysteresis loss is reduced. The eddy current loss is the joule loss of the induction current accompanying the electromotive force generated by the electromagnetic induction with respect to the magnetic field change, and, as the electric resistance of the material is smaller, the eddy current loss is reduced. Also, when a structural unit formed of the independent soft magnetic material further exists inside the material like a powder magnetic core, the eddy current is generated in the inside of each structural unit also, and, as the structural unit is smaller, the eddy current loss derived from the eddy current inside the structural unit is reduced.
In order to reduce the iron loss, there is a case where the powder magnetic core is manufactured by mixing the powder of the soft magnetic materials of two kinds or more including soft magnetic material having low coercive force. As the combination of the soft magnetic materials of two kinds or more, pure iron, Fe-3% Si alloy, Fe-6.5% Si alloy, Sendust®, amorphous alloy, and the like can be cited, and the mixture of these soft magnetic materials of two kinds or more is used as a magnetic core material. Among them, Sendust is a designation of an Fe-9.5% Si-5.5% Al alloy, is high in magnetic permeability and low in coercive force compared to general soft magnetic materials such as pure iron and the like, is therefore excellent particularly in AC magnetic characteristics in high frequency, and is suitable for the magnetic core material for high frequency. However, because Sendust is of a peculiar crystal structure, Sendust has a defect of being very hard and brittle material, powder compacting of the Sendust powder as a pure iron powder is done is difficult, and the Sendust powder is usually used so as to be dispersed into a resin in general. Although powder compacting of the Sendust powder is not impossible, because very high forming pressure is required, there are problems that the life of the forming mold is shortened and so on. Further, with respect to the magnetic core material for high frequency, although there are also an amorphous alloy (including microcrystal), permalloy, and the like, the amorphous alloy is a material higher in the hardness and harder in forming compared to Sendust, and permalloy contains much of Ni that is an expensive metal and is therefore significantly inferior to the pure iron, Si alloy powder and the Sendust powder in terms of the cost.
On the other hand, as prior arts, there are technologies that any two kinds or more of general soft magnetic powder such as the pure iron powder, Si alloy powder, amorphous alloy powder, Sendust powder and the like are mixed with each other, and the magnetic characteristic and formability are improved. For example, in Patent Literature 1, it is described that, when the amorphous soft magnetic alloy powder and the soft magnetic alloy powder (crystalline material such as Sendust and the like) are mixed with each other at a specific ratio with such grain size that the mode of the grain size distribution differs from each other by 5 time or more, the forming pressure is reduced, and the maximum magnetic flux density and the iron loss can be improved. Patent Literature 2 is an invention on mixing of pure iron and either of Sendust or permalloy. Patent Literature 3 is an invention of mixing of high compressive soft magnetic metal powder (pure iron powder or Fe-3% Si alloy powder) and ferro-alloy powder (Fe-9.5% Si alloy powder or Sendust powder), or mixing of them and soft ferrite. Patent Literature 4 is an invention on mixing of Sendust and highly expansible metal powder (pure iron powder, molybdenum-permally powder, Fe—Si alloy powder).